Electric power, particularly for relatively high-power applications, is frequently distributed (e.g., through an electric grid) in three overlapping alternating current (AC) phases that are 120 degrees out of phase with each other. Such power may be generated at a power plant, distributed through an electric utility's grid, and received and stepped down in voltage at transformers in electric substations. Generally, the power is carried by four conductors, or wires—one wire for each of the three phases, and a neutral or ground that is common to all three. The power may be further reduced in voltage (e.g., from medium voltage in the thousands of volts to low voltage in the hundreds of volts) and may be used as 3-phase power by various different loads or separated into multiple single-phase feeds and provided to loads (e.g., to computer server systems and other equipment in a computer data center).
For higher power AC distribution, the 3-phase power needs to be balanced for better efficiency and higher power utilization. Such balancing may be a challenge in power supplies that use power factor correction (PFC) connected to one or more 3-phase distribution transformers, and that have a neutral line that is earth-grounded so as to interfere with the ability to combine the outputs of the different PFC units together.